Hyperoxic lung injury reduces exogenous surfactant clearance in vivo

We studied the rate of clearance of treatment doses of radiolabeled calf lung surfactant extract, which was instilled into the lungs of young adult rabbits exposed to air (control) or 100% oxygen for 64 h. More than 75% of the instilled surfactant remained lung-associated at all time points up to 24 h post-instillation in both groups; however, significantly more of the labeled phosphatidylcholine (PC) remained in the alveolar wash of oxygen-exposed rabbits (44 +/- 9% in 100% O2 versus 27 +/- 5% in controls at 6 h and 27 +/- 2% in 100% O2 versus 6 +/- 1% in control rabbits at 24 h, p < 0.05). Less of the labeled PC could be found in type II pneumocytes isolated from the oxygen exposed animals than in control animals, both at 6 h (24 +/- 2 cpm/10(6) cells in O2 versus 38 +/- 7 cpm/10(6) cells in control) and 24 h (42 +/- 5 cpm/10(6) cells in O2 versus 70 +/- 12 cpm/10(6) cells in control) post-instillation. Type II cells from animals exposed to 100% oxygen also demonstrated significantly lower PC synthesis rates than cells from lungs of control animals. Interestingly, clearance of exogenous surfactant in rabbits exposed to 100% oxygen for 48 h, an exposure that does not cause significant type II pneumocyte dysfunction, was not different from control. We concluded that injury to type II pneumocytes may result in decreased clearance of instilled surfactant from the alveolar space and may be important in determining dosing regimens for the use of surfactant therapy in adult respiratory distress syndrome.